1. Field of the Invention
The present invention relates to a magnetic interface contaminant collector and more particularly to such a collector which is utilized with a leak detector positioned in an above ground storage tank for determining, by reason of changes in electrical or thermal conductivity, leaks in the above ground storage tank which contains liquid having a lower specific gravity and a lower electrical or thermal conductivity than water that may be present in the tank.
2. Description of the Prior Art
Leaks in large above ground petroleum product storage tanks containing liquids such as regular gasoline, light fuel oil, diesel fuel and regular gasoline are a serious problem to the petrochemical industry from the standpoint of both inventory losses and environmental degradation.
The large size of such tanks makes leak detection difficult. In this respect, a leak rate of one barrel per hour in a 100 foot diameter tank will produce a level change rate of approximately 0.01 inches per hour and a direct measurement of the level change at the surface of the liquid in the tank is difficult due to the resolution required and to thermal expansion of the liquid, the tank and the detecting apparatus.
Furthermore, acoustic emission methods of leak detection previously utilized provide results which are clouded by the weakness of the leak as an acoustic source and by signal attenuation in the liquid or in the tank shell. Furthermore, background noise from wind and thermal expansion also appear to limit the reliability of leak detection determinations utilizing acoustic emissions.
Experience has shown that all significant leaks in above ground tanks occur in the area of the tank bottom. Also, experience has shown that thermal conditions near the bottom of the tank are stable. Furthermore, surface waves and convection currents in the liquid are effectively dampened by the time they reach the bottom of the tank.
With these observations in mind, the leak detector disclosed herein and the method for using same utilize the environment adjacent the bottom of the tank for detecting leaks. The leak detector is adapted to be positioned in the stable zone adjacent the bottom of the tank.
Often fine particles of steel or rusted steel find their way into a mat of particulate and fibrous material at the interface between the petroleum product and the water in the tank. These particles can migrate to conductivity electrodes of the leak detector and foul them, severely hampering the operation of the leak detector. Accordingly, as will be described in greater detail hereinafter, according to the teachings of the present invention, a magnetic interface contaminant collector is provided in the above ground tank, particularly in association with the leak detector for preventing fouling and malfunction of the leak detector.